Method and apparatus for transmitting and reproducing sounds



May 11 1926. 1,584,451

H. c. HAYES METHOD AND APPARATUS FOR TRANSMITTING AND REPRODUCTNG SOUNDS Filed July v, 1925 Fly. l

Fly. 2

A DIA BATIC CURVE PRESSURE VOLUME I gmamto'v Hdri ey C". Hayes.

Patente diMay ll, 1926.

HARVEY c. HAYES, or WASHINGTON, DISTRICT 01? COLUMBIA.

mE'rHoD AND APPARATUS ron'raansmrrrme Ann REPRODUCING SOUNDS.

Application filed July 7,

My invention relates broadly to sound transmitters and reproducers, and more particularly to a method and apparatus for transmitting or reproducing sound free of 5 resonance effects and inherent distortion of the sound.

One of the objects 'of my inventionvis to provide a method of damping the diaphragm of a sound transmitter or reproducer whereby energy can be absorbed from the diaphragm at any desired point or points and which can be madeparticularly effective for absorbing the energy corresponding to any particular frequency at which the diaphragm is desired to be non-resonant.

Another object of the invention is to provide a construction of damping device for a diaphragm of a sound reproducer whereby the articulation of the reproduced'sound is considerably improved as compared with sound reproducers heretofore available.

A further object of the invention is to provide a simple construction of damping means for diaphragms whereby distortion vdue to the tendency of the diaphragm to vibrate at its fundamental or at monies is eliminated.

My invention finds particular application to sound transmitters and reproducers employed in telephonecircuits and in radio circuits eitheras a control for a radio transmission system or as a loud speaker at a radio receiver, but the principle may also be employed in connection with phonograph 85 diaphragms and other acoustic devices.

The invention will be more clearly understood by reference to the accompanying drawin in which: Figure 1 is a theoretical diap ragm used in. explaining the method employed in my invention; Fig. 2 is a theo retical curve for use in explaining the principle of the diagram in Fig. 1 Fig. 3 is :1

its harside elevation partially brokenaway and in section to the application of my invention to a telephone repr'oducer or loud speaker; Fig, 4 is a plan view of the bafiie plate of my invention, with the diaphragm removed and the cap member shown in section on line 4-4 of Fig, 3; Fig. 5 isda side view of the baflle plate and one form of support therefor partially in section; and Fig. 6 is a fragmentary vie'u of the reproducershowing 1923. Serial in. 650,183.

one form of adjusting means for moving the bafile plate relative to the diaphragm or rendering the different portions of the diaphragm non-resonant to undesired frequencies.

i The quality of sound reprdduced by diaphragms stimulated to vibrate by electrical means, as in the telephone, or by mechanical means, as .in the graphophone, is usually distorted to some extent because the diaphragm is always resonant at certain frequencies, the lowest of which is termed its fundamental, and. higher frequencies of which are termed its harmonics. The sound energy radiated from the diaphragm is much greater in proportion atthe resonant than at other frequencles and there is a tendency for the diaphragm to'continue vibrating longer at these frequencies after the driving force has ceased than it does at other frequencies. This-.may result in distorting the reproduced sound to something quite different from the original providing the original sound includes any of the resonant frequencies Moreover, the same distortion factors are usually present at both transmitting or recording end, for the diaphragm of the microphone used to transform the sound energy into electrical energy and the diaphragm that serves for driving the stylus in the recording mechanism for making graphophone records each have certain, definite frequencies at which the are resonant.

The location of the no es and loops that may be present in a diaphragm geometrically shaped actuated by a simple harmonic force applied at its center are known, as is also the relation of the pitchy)" resulting from each mode of vibration, to the fundamental;'and in case of any vibrating diaphragm this information can be obtained experimentally. An analysis of the sound emitted by 'a diaphragm driven'at "any frequency shows what harmonics are present and their relative intensity. This data together with a knowledge of the. possible forms inwhich the diaphragm may vibrate and the frequency of each mode of vibration,serves to localize on the diaphragm the areas that are unduly resonant and therefore responsible for the major part of the distortion. By my present invention, I provide means for absorbing energy from these regions on the diaphragm in such a way as to prevent it from being radiated as sound and accordingly a more faithful reproduction of the original sound results because of the removal of the distorting elements.

The principle involved in the present method may be understood from a consideration of Fig. 1 which represents a cylinder 1 fitted with an air-tight but frictionlesstheoretical piston 2, and closed at one end by a head 3 except for an opening a which can be varied in cross-section from zero to the -whole cross-section of the cylinder. For the purpose of illustration, assume that the opening 4 is in the form of the well known camera lens diaphragm whose exposed on open area is concentrically varied at will. Suppose now thevent 4 be closedand the piston pushed back and forth across its position of equilibrium. If the thermodynamic cycle through which the air in the pump chamber passes be considered adiabatic, that is where:

'PV: Constant as represented by the theoretical curve in Fig. 2 where P represents pressure and V the volume as it would be practically if the frequency of the piston were of the order of the pitch of ordinary audible sound, then the sum total of the work done on the piston by the gas in the cylinder or by the piston on the gas in the'cylinder will be zero and independent of the frequency' If, however, a small opening were made in the vent 4 some of theair in the cylinderwould escape on the instroke and some would return during the outstroke and in order to keep the piston moving with the same amplitude and frequency as much energy must be su plied to it as is used up in driving air bac and forth through the vent. It can also be shown that the amount of energy that the cylinder chamber absorbs from the-piston is dependent upon both the frequency of motion of the piston and the cross-section of-vent 4. It can also be shown that if the vent- 4 be made up of-several small holes instead of one large one the energy absorbed from the piston by. thev chamber will leave the chamber almost wholly as; heat, but that if one or more largeholes are useda considerable amount of energy will radiate frequency would eventually be met wherev the inertia of the piston and the restoring force introduced by the. air-tight chamber will be such as to make the natural period of vibration of the piston of equal value. Under such conditions, the sound input from the open end of the cylinder will have an intensity considerably greater in 'proportion than .it does for other frequencies. If, now,-t-he vent 4 be opened a proper amount, although it is preferable to use several small vents, energy may be absorbed from the pistonby the chamber to such an extent that the sound radiated at this frequency is much less out of proportion with respect to that radiated at other frequencies.

In case of a vibrating telephone diap iragm or other similar sound reproducing hereinafter described, for the narrowness of the crevice 7 between the diaphragnifi and the battle 6 prevent s'the air from moving readily in this direction. And, of course, the air will find difficulty in moving outward from the small cylinder described because of'the pressures already established by the moving diaphragm. Therefore, any small hole 8 or holes 9, 10, 11, or 12 made to perforate the bafile plate 6 within the area represented as the-end of the small cylinder will absorb energy from the piston area of the diaphragm 5. In other words, a small hole through the bafile plate at any point will absorb energy from a small area of the diaphragm opposite to the hole and closely adjacent thereto, and therefore the disturb ingresonance frequencies of a diaphragm can be ironed out, or in other words damped out by first determining to what mode of harmonic vibration they are due and then by placing a proper number of small holes or apertures through that portion of the bafiie plate that covers the vibrating loops.

The diaphragm 5 can be driven as a loud speaker by means'of electromagnet 14: connected in any voice frequency circuit as, for example, the output circuit of electron tube 15, the input circuit of which is supplied from a suitable circuit- 16 subjected to the voicemodulations. The baffle plate 6 is apertured at 17 to enable the electromagnet 14 to have its pole faces positioned immediately adjacent thediaphragm 5. The baffle plate 6 .is mounted ina' frame 18 by means of screws 19 radially" positioned at proper points about the 'peri hery of the frame 18. The frame, is provided with fine pitched threads 20 which cooperate with internal threads 21 within the housing 23 of the electromagnet. The diaphragm 5 is securely edge of the diaphragm whereby cap member 25 threaded at 26 will seat against the gasket and securely hold the diaphragm in position.

The baflie plate may be adjusted in position relative to the diaphragm by any suitable means. I have shown the frame 18 provided with a plurality of sockets 27 radially positioned about the periphery of the screw threaded frame. An elongated slot 28 is provided in the wall of the magnet housing 23, and a corresponding slot 29 is formed in the cap member. After the baffle plate 6 is assembled in position relative to diaphragm 5 it may be accurately adjusted by means of key 30, having one end fitted into some one of the sockets 27 and the baflie plate moved in a peripheral direction to adjust the distance between the bafiie plate and the diaphragm.

It will be understood that the details of the construction herein described are-notintended as limitations uponthe invention, but

merely as an illustration of one form which my invention may take. As heretofore set forth, the apertures 8, 9, 10, 11 and: 12 are located in the baflie plate at those positions where it is determined for a particulardiaphragrrr that undesired resonance effects should be eliminated.

It will be understood that I intend no limitations upon the present method and apparatus other than are imposed upon the 500 e of the appended claims.

l aving thus described my invention, what I claim and desire to secure by Letters Patent of the United'States is as follows:

' 1. The method of damping the diaphragm of a sound. reproducing device, consisting in absorbing energy from the diaphragm from.

a sideopposite to the principal sound delivery side of said diaphragm at any desired point or points corresponding to any par ticular frequency for which it is desired that said diaphragm be non-resonant. 2. The method of damping the diaphra of a sound transmitter or reproducer,wh1ch consists in absorbing from the diaphragm from a side opposite'the sound impressing or delivery side ofsaid diaphragm at a plurality of points throughout the area thereof those frequencies for which the diaphragm is desired to be rendered non-resonant.

3. The method of damping the diaphragm of a sound transmitter or reproducer, which consists in absorbing from different separated points on said diaphragm from aside opposite the sound impressing or delivery side thereof those frequencies for which it is desired that said diaphragm be rendered nonresonant.

4. In a sound transmitter or reproducer,

phragm for rendering said diaphragm nonresonantto particular frequencies.

5. In a sound transmitter or reproducer, the" combination of a diaphragm, means 10- bated directlymd'jacent said diaphragm at a .side opposite the sound impressing or delivery side thereof in a plane substantially throughout the area of said diaphragm for damping said diaphragm at particular ppints throughout said area for rendering frequencies.

a 6. A sound transmitter -or reproducer, comprising in combination a diaphragm, an apertured baflie plate mounted adjacent said diaphragm at a side op pressing or delivery S156 and located with respect thereto whereby said diaphragm is rendered non-resonant for particular he said diaphragm non-resonantto particularquencies. I

7. In a sound transmltter or reproducer, the combination w th a diaphragm; means plate located adjacent one side of said diaphragm opposite the sound impressing or delivery side thereof and supported by said means, said baflie plate having a substantial thicknessbeing apertured at a plurality of points throughout its area for providing energy absorbing air columns for rendering said diaphragm non-resonant to particular frequencies. I

8. A. sound transmitter and reproducer, comprising in combination a diaphragm, means for supporting said diaphragm, a baffle plate located immediately adjacentsaid diaphragm and supported by said means, sai baflie plate having a substantial thickness and being apertured at. a plurality of points throughout the area of said diaphragm for providing air columns for absorbing energy from different areas ofsaid diaphragm, whereby disturbing resonance effects may be substantially eliminated, and means for adjusting the distance between said diaphragm and said baflie plate.

comprising iii. combination a diaphragm, a

a plurality of points throughout the area of said diaphragm for providing air' columns for damping said diaphragm at different poosite the sound im- -90. for supporting said diaphragm, and a baflie support for said diaphragm, a baflie plate j carried by said support, said baflie plate having a substantial thickness and apertured atw sitions throughout its area for'eliminating undesired resonance effects, aslot in said supporting means, and means passing through said slot and into said baflie plate for adjusting the distance between said baffle plate and's'aid diaphragm.

10. A sound transmitter and reproducer,

comprising in combination a diaphragm, a

9. A sound transmitter and'reproducer,

support for said diaphragm, a bafile plate located adjacent said diaphragm and extending substantially throughout the area thereof, a

screw threaded frame for carrying said baffle plate, said baflie plate having a-substantial thickness and being apertured at a pluralityoir' points throughout the area'of said, diaphragm for providing air columns for absorbing energy frolfi difierent portions of said diaphragm whereby said diaphragm is rendered non-resonant to particular frequencies, and means secured to said frame on said,

baflie plate for adjusting the distance between said baflie plate and said diaphragm.

HARVEY G. HAYES. 

